Hey brains trust, I have a fridge that is not really normal for a yacht, it seems to be a bit more like a commercial fridge. So before I call a fridge guy I was hoping that someone where may have come across these pressure switches and how to set it.

I dont like the system and if money was not an object then I would replace it with something different. However we live in reality. So a brief run down of the system:
Runs on 240v, has one compressor and a water cooler for the refrigerant (not keel cooler). There are 2 eutetic plates in each compartment (fridge & freezer) and air does not flow between the compartments. I have recently replaced door seals in an attempt to make it more efficient. The 2 eutetic plates are at the back of the compartments and the difference between each compartment is just the refrigerant type. The system has only 1 control for both with changes in this effecting changes in both the fridge and freezer.

Since we have had the boat I think it cycles too much for a eutetic system based on talking to others with more traditional (Ozefridge) systems. With the settings that we are at, the fridge cycles for 20-25 minutes every 90 minutes. I have a couple of temperature sensors in the compartments and they are placed next to the plates. The fridge is currently reading 3 and the freezer -10. We would like them both a bit cooler as the freezer doesent actually freeze stuff so we are throwing out food. I know this is a catch 22 with upping the temperature meaning it will cycle more. I think that I need to increase the differential between when it kicks in and when it cuts out, but I am not sure how to do this.

Obviously we also only open it when we have to and try to keep it as full as possible etc etc

Here is a photo of the controls

I just did a quick Google & found this:
www.systemcontrol.com.au/brands/ranco/hvac-and-refrigeration/refrigeration-controls/pressure-controls/ranco-pressure-controls/22451005?s=

You'll need your Part Number to get the exact info but they are probably all similar - Click on the model > brochure

If you can't find a manual there maybe email or ring them for info.

Is this switch cycling the compressor, ???
Looking at the switch on the left, set at 2500 kpa,, that is the high pressure cut out with a manual reset to protect the compressor from excessively high pressure. no need to alter it
Looking at the dial on the right and the right hand scale that reads 200 kpa.The switch is set too cut in / start the compressor at 200kpa,,,
The dif in the left scale is set to aprox 150kpa, so the cut out / stop compressor is at 150 kpa lower than the cut in . 200-150= 50 kpa cut out.
These switches are usually set with gauges connected.
To increase the run time but maintaining the cut in pressure/temp. increase the value on the dif..
If you change the value in the right hand column (200kpa) to a lower value, the compressor will start and stop at an over all lower temp/ pressure maintaining the 150 kpa difference.
Caution
These values are usually inplace to protect the compressor and don't usually control temperature accurately.
Cool rooms that pump down often use their pressure switch to cycle the compressor but its forced to do so by a thermostat that turns a evaporator fan off or closes a liquid line solenoid. Small units that have these switches and are cycling the compressor with them often have other problems like low gas, excessive ice or a faulty thermostat.
Be Careful not to lower a value to the point that your compressor is pulling a vacuum, that can lead to many problems

Hi Dralyagmas
I was hoping that someone where may have come across these pressure switches and how to set it.

That's me, I suppose.

What you have here is a duel pressure control switch.
On the lest side is the high pressure cut out switch.
This is to protect your compressor from a high pressure situation and is factory set for your system and should not be altered.
What is a high pressure situation.?
In an air cooled condenser, the fan draws air through the condenser coil , cools the gas which condenses into a liquid and also draws air across the compressor which keeps it a little cooler.
If the fan stops,the gas pressure will rise higher than the compressor can handle. This will lead to a high amperage draw, a hot compressor and eventually compressor failure.
If the condenser is blocked buy a stray plastic bag or other obstruction, the gas pressure will rise higher than the compressor can handle. This will lead to a high amperage draw, a hot compressor and eventually compressor failure.
If there is a leak of refrigerant,, air will be sucked into the system,the gas pressure will rise higher than the compressor can handle. This will lead to a high amperage draw, a hot compressor and eventually compressor failure.
In the case of a water cooled condenser high pressure would be caused by pump failure, partial or complete blockage of cooling water or air in the system as per above.

The right side is a low pressure control switch.
This is to protect the system if there is a refrigerant leak and to control the refrigerant flow to allow a low amperage draw start up.
Again this is factory set for your system and should not be altered.The only time that this is altered by a technician is when the type of refrigerant is changed (i.e, the system ran on the old type of refrigerant, and is recharged with the new generation refrigerant).

The cut in/ cut out of your compressor is controlled by the thermostat in conjunction with the low pressure control.

In most (light duty) systems the thermostat cuts out at the set temperature and after the temperature in the cooled space rises a preset level (temperature difference = T.D.) it cuts back in again. The T.D is usually preset.
The location of the thermostat sensor (bulb) is important. If it is close to the cooling plate (evaporator) it will sense that low temperature and not the actual air temperature inside the cooled space.
If it is too far from the evaporator.it can lead to the evaporator freezing up and losing efficiency.

In your system with a dual pressure controller,I suspect the thermostat will open when it reaches the set temperature.
The open circuit will close a solenoid valve and stop the refrigerant flow.
The compressor will continue to run until it lowers the pressure to the preset level on the low pressure control switch and the compressor will cut out.
In this situation the pressure on the inlet (suction) and outlet side (discharged are almost balanced).
The thermostat will close after the cooled space temperature rises to the T.D., the solenoid open, the gas flows and the compressor will start in response to the setting on the low pressure control switch.
Solenoid valves


So. adjusting this will do nothing to getting your refrigerator operating at a lower temperature.

The 2 eutetic plates are at the back of the compartments and the difference between each compartment is just the refrigerant type. The system has only 1 control for both with changes in this effecting changes in both the fridge and freezer.
In my view 2 evaporators means two thermostats and two solenoids. If you are getting 3 degrees from you fridge that should be fine.
Ideally minus 15 is good for your freezer. Best setting are 1 degree and minus 17.

First question is has it always been like this or have you noticed a deterioration in cooling?
Check what temperature your thermostat is set at.
If you set it lower the system will run longer.
You can look for your freezer thermostat sensor and experiment with positioning it.
Another shot could be short of gas. If you have a sight glass in the system there should be no bubbles in normal running conditions. Some bubbles at start up are normal.

Hope this helps

gary

Select to expand quote

garymalmgren said..
Hi Dralyagmas
I was hoping that someone where may have come across these pressure switches and how to set it.

That's me, I suppose.

What you have here is a duel pressure control switch.
On the lest side is the high pressure cut out switch.
This is to protect your compressor from a high pressure situation and is factory set for your system and should not be altered.
What is a high pressure situation.?
In an air cooled condenser, the fan draws air through the condenser coil , cools the gas which condenses into a liquid and also draws air across the compressor which keeps it a little cooler.
If the fan stops,the gas pressure will rise higher than the compressor can handle. This will lead to a high amperage draw, a hot compressor and eventually compressor failure.
If the condenser is blocked buy a stray plastic bag or other obstruction, the gas pressure will rise higher than the compressor can handle. This will lead to a high amperage draw, a hot compressor and eventually compressor failure.
If there is a leak of refrigerant,, air will be sucked into the system,the gas pressure will rise higher than the compressor can handle. This will lead to a high amperage draw, a hot compressor and eventually compressor failure.
In the case of a water cooled condenser high pressure would be caused by pump failure, partial or complete blockage of cooling water or air in the system as per above.

The right side is a low pressure control switch.
This is to protect the system if there is a refrigerant leak and to control the refrigerant flow to allow a low amperage draw start up.
Again this is factory set for your system and should not be altered.The only time that this is altered by a technician is when the type of refrigerant is changed (i.e, the system ran on the old type of refrigerant, and is recharged with the new generation refrigerant).

The cut in/ cut out of your compressor is controlled by the thermostat in conjunction with the low pressure control.

In most (light duty) systems the thermostat cuts out at the set temperature and after the temperature in the cooled space rises a preset level (temperature difference = T.D.) it cuts back in again. The T.D is usually preset.
The location of the thermostat sensor (bulb) is important. If it is close to the cooling plate (evaporator) it will sense that low temperature and not the actual air temperature inside the cooled space.
If it is too far from the evaporator.it can lead to the evaporator freezing up and losing efficiency.

In your system with a dual pressure controller,I suspect the thermostat will open when it reaches the set temperature.
The open circuit will close a solenoid valve and stop the refrigerant flow.
The compressor will continue to run until it lowers the pressure to the preset level on the low pressure control switch and the compressor will cut out.
In this situation the pressure on the inlet (suction) and outlet side (discharged are almost balanced).
The thermostat will close after the cooled space temperature rises to the T.D., the solenoid open, the gas flows and the compressor will start in response to the setting on the low pressure control switch.
Solenoid valves


So. adjusting this will do nothing to getting your refrigerator operating at a lower temperature.

The 2 eutetic plates are at the back of the compartments and the difference between each compartment is just the refrigerant type. The system has only 1 control for both with changes in this effecting changes in both the fridge and freezer.
In my view 2 evaporators means two thermostats and two solenoids. If you are getting 3 degrees from you fridge that should be fine.
Ideally minus 15 is good for your freezer. Best setting are 1 degree and minus 17.

First question is has it always been like this or have you noticed a deterioration in cooling?
Check what temperature your thermostat is set at.
If you set it lower the system will run longer.
You can look for your freezer thermostat sensor and experiment with positioning it.
Another shot could be short of gas. If you have a sight glass in the system there should be no bubbles in normal running conditions. Some bubbles at start up are normal.

Hope this helps

gary

Nice one Gary this is great.

Not seen a deterioration but we have only had the boat 12 months. The previous owner seemed to be a marina boat connected to shore power a lot and the fridge and freezer was cooler but cycled almost every hour. When they cruised they used a generator a lot. I had a fridgey come and look at it and he dialled it down but didnt explain what he was doing. He didn't think it was short of gas though. He suggested I just experiment with the pressure diff setting, but I was hesitant until I understood it.

I cannot find a thermostat connected to the system, but there is a sensor and on one of the plates with the wire. I have to chase that down but I have been through all of the boat extensively and cant find a thermostat. I have put dual temperature sensors in each compartment www.catch.com.au/product/avanti-digital-2-zone-fridge-freezer-thermometer-white-2301509/?offer_id=13886786&gclid=Cj0KCQjwncT1BRDhARIsAOQF9LkZJzN7qWDomQm4y96IOJrVzIRaoHDl5wugBReAlzcZXbn9qKcllbYaAoJMEALw_wcB

I have placed the sensors right next to the plates but there is a difference between the back of each compartment and the front.

I think I will up the diff and see what happens.

Thanks for the great input